1. Field of the Invention
The present invention relates to an optical fiber flexible multi-wavelength filter and a method of controlling a wavelength of a spectrum using the same. More specifically, the present invention relates to an optical fiber flexible multi-wavelength filter showing a variety of transmission characteristics of a spectrum and a method of controlling a wavelength of a spectrum using the same.
2. Description of the Related Art
In an optical communication system, multi-wavelength light sources or all-fiber wavelength-selective filters have received much attention as the main devices used for satisfying the demand for increasing bandwidth.
Among such devices, optical fiber filters are used as a core element for wavelength routing in a wavelength-division-multiplexing network. In the optical fiber filters, it is important to maintain the wavelength space of the filter, and precisely adjust the position of the absolute wavelength to be within an ITU-grid standard wavelength of a wavelength division multiplexed network.
Meanwhile, many studies have been made on optical fiber multi-wavelength filters because of the ease of design and use thereof, and a mechanical method and a polarization control method, etc. have been proposed in order to control the absolute wavelength of a channel of the optical fiber multi-wavelength filter.
Optical fiber multi-wavelength filters may be fabricated using a high-birefringence optical fiber in an optical path of a Sagnac interferometer, which is an interferometer configured in such a manner that two waves which propagate along the same optical path, but in opposite directions, interfere with each other. Sagnac interferometers have several advantages, such as a simple structure, ease of use, and a variety of wavelength selection characteristics.
When an optical fiber multi-wavelength filter based on a polarization-diversity loop is fabricated in the optical fiber multi-wavelength filter using a polarization beam splitter instead of an optical fiber coupler, properties associated with wavelength switching including wavelength interleaving may be obtained.
In particular, in the optical fiber multi-wavelength filter based on the polarization-diversity loop, a high order transfer function capable of obtaining various transmission spectra can be generated using several strands of high-birefringence optical fibers.
For example, a Solc type filter implements the high order transfer function via connecting high-birefringence optical fibers to generate an angle difference (i.e., azimuth) between principal axes of high-birefringence optical fibers neighboring each other and having the same length. In addition, a Lyot type filter implements the high order transfer function by connecting high-birefringence optical fibers neighboring each other to have the same length and connecting a polarizer between high-birefringence optical fibers.
Existing Solc type optical fiber multi-wavelength filters based on a polarization-diversity loop are fabricated by fixedly connecting two high-birefringence optical fibers having the same length in such a manner that an angle difference between the principal axes becomes 45° using a fusion splicing method. In the Solc type optical fiber multi-wavelength filters based on a polarization-diversity loop, an interference spectrum in a flat transmission band mode and an interleaved result of the interference spectrum can be obtained among a first interference spectra.
However, the above-described existing method cannot implement a transfer function showing interference spectra other than the first interference spectra, and only the results of interleaving in a flat transmission band mode among the first interference spectra have been reported.